Endothelial cells play central roles in the development, growth, maintenance and repair of the vascular system. Their interaction with the organized underlying and surrounding substratum in part, directs or influences the endothelial cells' responses; yet very little is known about these complex interactions and the mechanisms by which they mediate their effects. The aims of this proposal are to compare and contrast the responses of large vessels (arterial) and capillary endothelial cells to injury and to elucidate the complex roles of the extracellular matrix in endothelial cell biology. Both tissue culture models (which have been developed during the last three years) and in vivo models will be used. Specifically, the organization and functional domains of the extracellular matrix (ECM) will be probed using monoclonal antibodies, biochemical and rotary shadowing methods in order to elucidate the roles of selected domains in influencing endothelial cell biology including attactment, spreading, proliferation, migration and differentiation. Furthermore, the complex interactions of the endothelial cells with their underlying ECM will be studied using antibody probes directed against selected receptors (laminin, fibronectin, specific collagens). Plasmalemmal membrane fractions will also be utilized in solid phase binding assays. We will elucidate the organizations and dynamic changes in the endothelial cell (EC) cytoskeletons as functions of varying the underlying substrata in the resting and "wounded" states and correlate ECM-induced changes in the cytoskeleton with perturbations in EC attachment, spreading, proliferation, migration and differentiation. Lastly, we will correlate the changes observed in luminal and abluminal plasmalemmal microdomains with ECM-induced changes in localization, organization and composition of specific cytoskeletal components including fodrin, bands 2.1 and 4.1, vimentin, tubulin and actin. These studies will allow for a better understanding of the important, if not pivotal, interactions between the EC surface, the organized ECM and ECM-induced changes in the cytoskeleton which direct cell function as well as morphology.